Wattage ratings for controls?

[Russel Nash]

Hi there,

Just wondering what the controls (rheostat?/thermostat?) on either the RCBS pro melt or the Lyman Mag furnaces are rated for?

I was thinking about ordering a new control for one and cobbling it together for another use entirely.

Thanks!

[montana_charlie]

There should be a data plate on your melter(s) which shows the electrical characteristics.
It is common to see the wattage included in that data, on high temperature devices.
CM

[454PB]

I don't own either of these pots, but I recently read an ad for the RCBS Pro-Melt and it said it was 800 watts.

[Echo]

I believe they are neither rheostats or thermostats - they are 'controls', similar to the control on an electric blanket. They simply 'control' the amount of power sent to the heating element - our furnaces are calibrated to show the approximate temperature developed by a certain amount of power. I think...

And light dimmers work fine on most 10-lb furnaces. Might be a little light for a 20-pounder. I have a light dimmer built in to a socket over my bench, and hooked up to one of the outlets. Thought it would be a smart thing to do many years ago, and have used it, even for casting furnaces. My new little guy doesn't have a control, so I must use the dimmer on the socket.

[cajun shooter]

The paper work with my RCBS states that it has an industrial strength thermostat.

[montana_charlie]

I believe they are neither rheostats or thermostats
Why do you believe they are not thermostats?

They simply 'control' the amount of power sent to the heating element
What do you think a rheostat does?
CM

[Echo]

A rheostat is simply a variable resistor and would have to handle MUCHO power for this job. And power would be burnt up in the resistance. Not feasable... OK for a volume control on a radio, but not for the kind of power we need.

A control operates on heat. It is either on or off. As we advance the control to a higher level, it puts more strain on a bi-metal contact that completes the circuit to the heating element. The current passing through the contact warms it up, causing it to warp. When it gets hot enough, it pulls away from the matching contact, breaking the circuit. No more power to the element. Then, as the bi-metal strip cools down, it 'unwarps', remaking contact, and sending power to the element again. The dial is calibrated in degrees, but that calibration depends on reliability of construction and fabrication of the control itelf. When the dial is set very low, little strain is placed on the bi-metal strip, and it pulls away easily. When the dial is turned higher, the contacts stay 'made' longer, sending more power to the element, heating the alloy more.

A thermostatic control would need a probe going into the alloy, so that control would depend on the actual temperature of the alloy - our furnaces don't have thermostat controls, even though they may claim to.

I think...

[Lee W]

I know of the thermostat in the RCBS. It is a 10mm stainless steel bulb type thermostat with a 6% of scale accuracy. (+-30F in this case)
The switch can handle 16 amps at 230 volts, so 3680 watts.

[MT Gianni]

Easy ED, I believe that the thermostat senses heat from the pot wall. If it has a bi-metal it is designed to warp a certain amount at a certain temperature. It senses the wall temp at a known distance measuring heat at that point. Gianni

[montana_charlie]

How abut this, Ed...

A rheostat is a two-contact variable resistor. It is rated for (capable of handling) the full current load of the circuit it operates in. Rheostats are primarily used for 'current control', therefore are chosen for high current devices.
A potentiometer is a three-contact variable resistor which operates as a 'voltage divider' within it's circuit. As such, it taps off a portion of the voltage potential felt across the two outer contacts, and is most commonly used adjust the voltage in volume control circuits, and other low-current applications.

A thermostat is a temperature-controlled switch. When a target temperature is reached, the switch opens to interrupt (or closes to allow) current flow in the controlled device.

A temperature-controlled switch can use pressure (in a bulb sensor thermostat) or radiant heat (in a bimetal strip thermostat) which actuates the switch contacts mechanically.

A device such as a K-type sensor can be used to electronically control a heating circuit by (1) operating switch contacts that are part of a relay...or (2) by varying the amount of current flow in a circuit...much the same as a rheostat would do in a 'manual' control system.

The bi-metal strip found in the thermostat used for a typical lead melting pot does not carry current. It simply pushes the switch contacts open, mechanically, when radiant heat causes it to bend. Turning the knob to a particular position determines how far the strip must bend before the contacts open.

CM

[Echo]

I mostly agree, CM. I was an electronics type in a prior incarnation (Second Class phone, General Class ham, as well as instructor), so know the diff between rheo & pot. My point was that a thermostat needs feedback from the controlled point. I didn't know about the RCBS system, that apparently actually uses a thermostatic arrangement.
When I had to repair my old SAECO furnace, I got a good look at the control. There is no clear shot for the retort heat to hit the bi-metal. The outer shield around the retort and element are continuous inside of the housing. And the mains went directly to the bi-metal, through the contacts, to the element. I just don't see that there would be enough heat 'signal' from the pot to activate the control.

[montana_charlie]

When I had to repair my old SAECO furnace, I got a good look at the control. There is no clear shot for the retort heat to hit the bi-metal. The outer shield around the retort and element are continuous inside of the housing. And the mains went directly to the bi-metal, through the contacts, to the element.
Consider this, Ed. As you know, maximum current flow will create maximum heat in a conductor (whatever 'maximum' is for the circuit in question).
If current for the heating element is routed through the bi-metal strip, the strip will get hottest when the most current is flowing.
The time when maximum current is needed is when you turn on a cold pot full of lead.

Does it make sense to heat that bi-metal strip with current flow, causing it to open the contacts, shutting off power to the element, at the exact time when the most heat is required?

I have to believe your Saeco thermostat did not have a current path through the bi-metal strip...even if it looked like it did.
As it happens, I have an old Lyman pot which is probably identical to your Saeco. I have not had occasion to dig into the pot shroud, but I will eat crow if I ever do...and discover a situation such as you describe.

I just don't see that there would be enough heat 'signal' from the pot to activate the control.
The engineer who chose the thermostat knows how warm (or hot) the area around the pot should become. He will have chosen a bi-metal strip which operates in that environment.

The one in the thermostat hanging on my wall operates in a range of temperature that falls between 50 and 80 degrees.

I'll bet the one in your old Saeco pot got at least that warm...
CM

[Echo]

Well - When the switch closes, it sends maximum current through the element. It is just a silly on/off contact, and the resistance of the element is basically fixed, so when the contact is 'Made', a fixed value of current flows, depending on the line voltage. There may be a variance in element resistance due to element temperature, but I doubt if is significant.

So with the knob turned way down, the contacts are Made maybe 10% of the time - when turned way up, maybe 90%, or even 100% of the time. This is what determines the temperature in the pot - the duty cycle of the control. 115 volts for 10% of the time, versus 115 volts 90%, or 100%, of the time.

I think...

And the thermostat on your wall, like mine, is a true thermostat, in that it reads the temp of the air in the house, and depending on the setting, decides to send current to the furnace/AC as needed, and shutting it off when no longer needed. I maintain that the control on our 10-lb furnaces simply controls the duty cycle of the system, sending more or less power to the element, not as needed, but as set by the knob.

Perhaps someone who has more creds than I can either support my position or set me straight.

[MT Gianni]

Ed, Wall t/stats are bi-metal or mercury filled with the exception of the new electronics. The bi-metal warps at about a 2-3 degree swing while the mercury, if level, react to a 1-1 1/2 degree swing. That is why the older mercury were more expensive and more comfortable. They run on either 24 volts making a relay or millivolts powering a load directly.
A bi-metal switch is literally two pieces of metal bonded together that warp at different rates. They have to be heat sensing to bend. They may be flat, disc or spiraled but they all operate from heat by their definition as a bi-metal.

[montana_charlie]

Perhaps someone who has more creds than I can either support my position or set me straight.

I was an electronics type in a prior incarnation (Second Class phone, General Class ham, as well as instructor),
Where did you instruct, and what did you teach?

If it's worth anything as far as cred goes...
I taught electronics at the Air Force Technical School in Biloxi, MS (for five years) as my full-time job.
Some of that was teaching basic theory and practical application to recruits...and the rest was teaching new systems to journeyman-level technicians coming in from the field for advanced training.

While the goal was to fine tune the thermostat to operate a bit more reliably, we went through the operation of a melting pot thermostat in this thread.
http://castboolits.gunloads.com/showthread.php?t=7204&page=2

There is a pretty good picture in Post #29, and an explanation of how it works in Post #30.

Does that thermostat resemble the one in your Saeco?
CM

[Echo]

Taught Guided Missile Control Systems electronics @ Lowry, Orlando, Hahn, and Bitburg, '54 to '62.

And it comes to my attention that the Lee series undoubtedly use the dimmer-type controls, that is, electronic vs. bi-metal.

[DLCTEX]

My Lee pot uses a bi-metal switch, as does my Lyman 20#.

[ddeaton]

Nash, what are you going to use it for? You need to know the temp range and the current rating of the load you are going to control. Then pick a temp controller in that range. I work with temp controls all the time in manufacturing. Not all are cost effective for us at home, but there is some nice stuff out there. Is there a need for a more accurate controller in our hobby?

[Echo]

Well, it s a surprise that the Lee pots use a bi-metal control. Makes one wonder how they get their feedback signal from the heat of the alloy, given that it is separated by an air gap and an aluminum housing... At least the 10-lb and under are...

[Russel Nash]

ddeaton wrote:


Nash, what are you going to use it for?

It's for a birdshot maker I am tinkering with.

I made it from "scratch".

I finally found a heating element of the right shape that will jive up with the "ladle", which is a 10" wide piece of channel iron.

The circular shaped stove top elements I was using are usually 6" or 8" in diameter. The highest watt rating I think I found was an 8 inch one at Home Depot, and was listed at 2,100 watts.

The problem with the circular ones under a 10" piece of channel iron was that the corners would get too cool, and if the "drippers" spit out any lead at all, what they produced was crap. :x

So let this be a lesson to you all, bigger is not necessarily better when it comes to birdshot makers.

I found a element that I like that is more square-ish and is just the right width for my 10" wide channel iron ladle.

The thing is it will draw 3,000 watts.

So I was hoping to cobble either an RCBS or a Lyman controller to it. But if they are listed at only 800 watts, it sounds like they aren't good enough. :sad:

See, if you get the shot too hot, once it hits the coolant, it explodes and turns into "popcorn shot". You get the lead melt too cool and the drippers will "freeze up" or they produce crappy shot too.

The other thing too, especially what I hear about the Littleton shotmakers is there isn't enough thermal mass or "mometum" there to be able to take on a cool or room temperature ingot. You stick an ingot too fast into a Littleton and it sucks all the heat of the melt and the drippers start spitting out bad shot or they freeze up entirely.

So that's why, kinda, I went with such a large piece of channel iron. I also figured I could mount more drippers across it too. And that's why I also like this new square-ish 3,000 watt element that I have. It shoud have enough gumption to keep melting lead ingots without freezing up the drippers.

I was hoping to rig some sort of control to it that through trial and error most likely I can dial in some temperature setting, set a stack of ingots in a "magazine" of some sort so it self feeds, turn it on, and walk away from it.

I was hoping I could make a birdshot maker that I didn't need to baby sit all the time.

I did search via google several times for temperature controllers, even pottery kiln controllers, but I am just not electrical or techno savy enough to plunk down that kinda of money for.

At first, I thought a 110V dimmer switch (like for your dining room chandelier) might work, but I think the element I have will draw too many amps for the switch.

So I figured the RCBS or the Lyman controls would be next best thing.

Your typical electrical oven controllers are out because they are only good up to 525 degrees F.

I have also been looking into getting one of those stainless steel shield K-type thermocouples for my digital read out thermometer. At least then, if I do find the right combination of melt temperature and head pressure which is producing really good shot, I can record the temp, and if I do find a control knob, I can write on the dial face what that temp is for next time.

Thanks a bunch for the replies.

I'll keep looking.

[Russel Nash]

Lee W. wrote:


I know of the thermostat in the RCBS. It is a 10mm stainless steel bulb type thermostat with a 6% of scale accuracy. (+-30F in this case)
The switch can handle 16 amps at 230 volts, so 3680 watts.

Oooppsss... I guess I didn't see your post on the first read through of this thread.

Hmmn... maybe the RCBS controls are an option still.

[Russel Nash]

I called RCBS today.

The controller, they said, was $42.

I will have to take a peek inside my RCBS Pro-Melt furnace to see what else I would need to buy.

They also said the 110V and the 230 V models take the same controller. :confused:

I guess it's all a matter of how the whole sha-bang gets wired together. :confused:

[Echo]

It seems that RCBS uses an actual thermostat - if so, it responds to the temperature of the alloy, and not the duty cycle as a controller would, so mains voltage would have little effect, other than max load allowed.

Check at a plumbing or HVAC supply for a heavy duty dimmer/controller capable of carrying 8-10 amps (whatever your heating elements will draw). Can probably buy one a lot cheaper than $42...

[DLCTEX]

I think the simplest way to switch the 3000 watt element would be to use a magnetic relay for switching and then any of the thermostats will handle the small load of the magnetic coils.

[Russel Nash]

Now... you two have got me scratching my head. :confused:

[Lee W]

You could get these items:

http://auberins.com/index.php?main_page=product_info&cPath=1&products_id=14

http://auberins.com/index.php?main_page=product_info&cPath=3&products_id=22

http://auberins.com/index.php?main_page=product_info&cPath=2&products_id=30

And I and others here would help hook it together.

[Russel Nash]

You guys keep this up and it's gonna turn into the mother of all birdshot makers.

:mrgreen:

Thanks for those links.

[moptop]

Hello to all! This is my first time posting here and I don't want hijack this thread but I just wanted to add a little info on controls/thermostats. I am an appliance tech by trade and if you are needing a way to regulate temp on an electric element I think I can help. Just use a surface burner control from and electric stove. It's called an infinite switch and will simplify your build, espeically since you are going to power it with 240 volts. They work as explained above in this thread by cycling on and off by means of monitoring the current draw of the element through a bi-metal contactor. Or if your want a more precise control of your pot temp you can use a bulb type oven thermostat also obtainable from an older style electric stove. Only 2 contacts, you hook it up like a light switch. Now you will have to play with the placement of the bulb because these are only designed for temps between 200 and 500 degrees. I've never seen anyone who would want to cook food at 700+ degrees,...unless she's really pissed at the husband for buying another gun!!

I built my own lead melting pot from scrap parts and it works great. I used a small stainless bowl, a defrost heater from a refrigerator, and a coffee can as a heater box.
Nothing fancy but it gets the job done and is very easy to build.

http://beta-api.joggle.com/media/?media_id=377124F2E57C4CD08BBF0C1CFBBF651B&sitename=moptop

[Russel Nash]

^^^ Thanks Moptop!

And welcome to the forums!

I still need to give RCBS a call back to see if their controller does include the thermocouple. I posted pics of the innards of their Pro Melt in another thread.

Yeah, I had thought about the oven controller too, but the 500 degree max oven temp thing threw me off.

I guess if I put the thermocouple in contact with another part that wasn't so close to the melt or to the element, and was more in the range of 400 or 500 degrees that might work.

One junk yard I called to ask about old electric ovens, the gal said something to the effect because of legal reasons the owner might not want you out there scavenging for stuff.

:confused:

:(